The present invention relates to improvements in processes like that disclosed in U.S. Pat. No. 3,835,214 to Hurst, et al. which patent is incorporated herein by reference for recovering uranium from wet process phosphoric acid. The phosphoric acid is an intermediate product of the wet process for producing phosphate fertilizer by treating uraniferous phosphate ores with sulfuric acid. The phosphoric acid contains sufficient uranium to warrant its recovery.
As disclosed in the above-mentioned patent, the uranium is conventionally recovered from the phosphoric acid solution by two liquid-liquid solvent extraction stages. In the first stage the uranium is reduced to uranous form and recovered from the solution with a liquid-liquid solvent extraction agent consisting of a mixture of mono- and di-(alkyli-phenyl) esters of orthophosphoric acid (OPPA) dissolved in an inert organic solvent and the loaded agent subjected to an oxidative strip with phosphoric acid and an oxidizing agent it is postulated that the extraction agents of this process work by ion exchange, and they are therefore referred to in the following discussion as "ion exchange agents", and the liquid-liquid solvent extraction steps are referred to as "ion exchange steps". The loaded agent is stripped and subjected to a second liquid-liquid solvent extraction (ion exchange) step followed by a further procedure to recover product uranium oxide, all as disclosed in the above mentioned patent and as improved in our copending U.S. patent Ser. No. 833,247 filed in the U.S. Patent and Trademark Office on Sept. 14, 1977.
The use of the mixture of mono- and di-(alkyl-phenyl) esters of OPPA as an extraction agent for the recovery of uranous uranium from wet process phosphoric acid is fully discussed in an article entitled "Recovery of Uranium From Wet-Process Phosphoric Acid by Extraction with Octylphenylphosphoric Acid," F. J. Hurst and D. J. Crouse, Industrial Engineering Chemistry, Process Design Development, Volume 13, Number 3, 1974, pages 286-291. More recently, the topic was discussed by F. J. Hurst in a paper entitled "Recovery of Uranium From Wet-Process Phosphoric Acid by Solvent Extraction," presented at the AIME Annual Meeting in Las Vegas, Nevada--Feb. 22-26, 1976. It is stated in both articles that in process use of the OPPA mixture, the mono-OPPA is lost to the aqueous preferentially to the di-OPPA. Mono-OPPA distribution loss to the aqueous phase is about 25 parts per million parts of aqueous whereas the distribution loss of the di-OPPA is negligible. Preferential loss of the mono-OPPA from the OPPA-organic mixture results in imbalance of the ratio of di- to mono-component. Table 1 summarizes experimental data developed by F. J. Hurst which support the above statements. As can be seen in Table 1, the uranium extraction coefficient was about 30 in extractions with an equimolar mixture of the mono- and di-OPPA compared to about 2 with either component alone. Unchecked preferential loss of the mono-OPPA component from the OPPA-extraction agent results in significant additional expense because of the necessity of continuous repletion of the mono-OPPA component during continuous operation of the process.
Accordingly, it is an object of this invention to provide an improvement in the stated uranium recovery method, the improvement being the recovery of the mono-OPPA component from the aqueous with subsequent recycle of the mono-OPPA components to said OPPA-organic extraction mixture.
TABLE 1 ______________________________________ Effect of Mole Ratio of Mono- and Di-OPPA on Uranium Extraction* OPPA Concentration (M) Uranium Extraction Coefficient Mono- Di- (E.sub.a.sup.o ) ______________________________________ 0.200 -- 2.1 0.175 0.025 5.3 0.150 0.050 10 0.125 0.075 16 0.100 0.100 30 0.075 0.125 30 0.050 0.150 37 0.025 0.175 30 -- 0.200 2.3 ______________________________________ *F. J. Hurst, "Recovery of Uranium from WetProcess Phosphoric Acid by Solvent Extraction," AIME Annual Meeting, Las Vegas, Nevada, February 22-26, 1976, Preprint Number 76B-66, p. 21.